This Week in Science

Science  06 Jan 2006:
Vol. 311, Issue 5757, pp. 12
  1. Bring Your Own Bacteria


    Attine ants of the Americas cultivate gardens of fungi, but these food sources can be parasitized by other fungi. The ants ward off fungal parasites by means of antibiotic-producing bacteria. Currie et al. (p. 81) now show that the ants are so dependent on the bacteria that they have special anatomical structures that carry the symbionts on the cuticle surface and that may supply nutrients to the bacteria. The organization of these structures varies with the ant species, possibly reflecting variable co-evolutionary pressures.

  2. Money for Nothing

    Rarely does one encounter someone who isn't at least slightly interested in money and in how to get more of it in social exchanges. Camerer and Fehr (p. 47) review the economic consequences when two kinds of nontraditionally behaving subjects—those exhibiting bounded rationality and those who are nonselfish—enter into games with exclusively self-interested individuals (the completely rational “Economic Man”). It seems that strategic incentives can enable a minority of irrational players to render the entire market irrational, but there are also conditions where a minority of rational traders can make the entire market rational.

  3. Quiet Cuprate Qubits


    Macroscopic quantum effects have been reported with a number of conventional (metallic) superconductors. The use of these effects in quantum computing must contend with signal losses caused by decoherence, an inherent problem as the logical elements (qubits) in these systems cannot be uncoupled from its environment. Recent theoretical proposals have suggested ways to isolate the qubit from its electromagnetic environment and make it less subject to decoherence, and the d-wave symmetry of the ceramic hightemperature superconductors (HTSCs) may provide a route to such a quiet qubit. However, it has been assumed that low-energy quasiparticles in HTSCs would destroy any benefits of that environment decoupling. Bauch et al. (p. 57) now demonstrate an HTSC device with sharp energy levels that exhibits the macroscopic quantum effects seen in their well-behaved metallic cousins. This result also indicates that the dissipation mechanisms in the HTSCs need to be rethought.

  4. Arm's Length

    Mapping the dimensions of the Milky Way with precision is still a daunting task. Xu et al. (p. 54, published online 8 December 2005; see the cover and the Perspective by Binney) have used precise images of radio sources in a star cluster to fix the distance to the nearest spiral arm from the Sun using trigonometric parallax, the small shift in apparent position as Earth moves between opposing points in its orbit. Using the Very Long Baseline Array, the authors detected this shift for radio sources in a young star cluster that forms part of the Perseus Arm of the Milky Way. The star cluster has extra anomalous motions beyond the simple rotation of our galaxy about its center that may be consistent with spiral density-wave theory.

  5. Forces Underlying Regime Change

    A major change in the marine ecosystem of the North Pacific Ocean that occurred in the mid-1970s, often referred to as a “regime shift,” may have been a natural variation in oceanatmosphere conditions or the result of anthropogenic global warming. Field et al. (p. 63) examined the abundances of different species of planktonic foraminifera (forams) in sediments from the Santa Barbara channel. Cooler water species began a marked decline in abundance relative to warmer water types around 1960, when deeper penetration of near-surface warming of the ocean began. The proportion of tropical and subtropical forams was not as high any time during the past 1400 years as during the late 20th century. Thus, anthropogenic forcing appears to have been an important component of this regime shift.

  6. Short Stout Snout

    Crocodiles evolved during the late Permian and early Mesozoic and became widespread during the Cretaceous, and one common characteristic has been their large, long snout containing numerous teeth. Gasparini et al. (p. 70, published online 10 November 2005; see the Perspective by Clark) now describe an unusual crocodyliform from Patagonia dating to about 140 million years ago. It has a stout head and jaw, but each jaw contains only about one dozen large serrated teeth. This morphology is similar to that of some terrestrial archosaurs and greatly expands the evolutionary morphology of crocodyliforms.

  7. The Making of the Modern Cat

    Unraveling the relatively recent speciation events that led to the modern cat family, which includes lions, tigers, clouded leopards, and domestic cats, has been hampered by an incomplete fossil record and a lack of distinguishing skeletal features. Johnson et al. (p. 73) analyze an extensive array of X-chromosome, Y-chromosome, and mitochondrial DNA sequences sampled from all 37 extant cat species to produce a phylogenetic tree that resolves the eight major lineages of cats. Modern cats appear to have originated in Asia 10 million years ago and undertook a series of 10 intercontinental migrations that correlate with major fluctuations in sea level.

  8. Depression, Serotonin, and p11

    Serotonin is an important modulator in a large number of physiological and pathological brain states. Among the many different serotonin receptors, the 5-HT1B receptor plays a crucial role in regulating serotonin neurotransmission. Svenningsson et al. (p. 77; see the Perspective by Sharp) investigated the role of a protein, p11, which appears to interact with 5-HT1B receptors, in depression and antidepressant treatment. 5-HT1B receptor function depended on p11 expression, and p11 levels were low in depressive states both in animal models (transgenic overexpression and knockout lines), as well as in human postmortem brains from depressed patients. In contrast, p11 levels were increased by antidepressant drugs and electroconvulsive treatment.

  9. But Will You Know Me Tomorrow?

    The variety of people with whom we interact extensively changes with time, and a single snapshot cannot provide a complete picture of a dynamic network. Kossinets and Watts (p. 88) have used a data set of e-mails between students, faculty, and staff at a large university, in combination with encrypted information about personal attributes and classes attended. They assembled a quantitative picture of how the strength of interactions depends on similarities between the individuals and how the interactions change with time.

  10. To Grow, or Not to Grow

    Adverse growth conditions, such as excess drought and salinity, tend to cause stunted growth in plants. Achard et al. (p. 91) now show that this growth restraint is an actively controlled process, not simply a by-product of disrupted metabolism. The growth restraint is imposed by DELLA proteins, normally localized to the cell nucleus. Arabidopsis has five related DELLA proteins encoded in its genome. The DELLA family of proteins seems to integrate hormonal and environmental signals in order to fine-tune the balance between growth and survival.

  11. Organizing the Root


    Specification of cellular fate in the Arabidopsis root depends on signaling by the hormone cytokinin. Mähönen et al. (p. 94) have now analyzed how cytokinin regulates and stabilizes choices in vascular cell fate. Protoxylem differentiation is a default choice, a direction that is blocked by cytokinin. The AHP6 locus promoted protoxylem differentiation and encodes a protein with resemblances to phosphotransfer proteins except for an amino acid residue critical for phosphotransfer. Nonetheless, it inhibits a cytokinin-directed phosphorelay system. AHP6 expression is spatially localized such that it can block cytokinin function in specific regions, thus allowing protoxylem specification in those locations. Cytokinin and AHP6 interact together in a feedback loop to create specific cellular domains that remain less responsive to cytokinins.

  12. Yin and Yang on the Reef

    The effects of “no-take” marine reserves remain poorly understood and controversial. Mumby et al. (p. 98; see the Perspective by Hoegh-Guldberg) studied the effects of the recovery of a top predator in a large and long-established coral reef reserve in the Bahamas archipelago. As the predator (the Nassau grouper) increased in abundance, the species composition of its prey (parrotfish) shifted toward species too large and fast to be caught and eaten by the grouper. Parrotfish are a key component of the reef food web because, as algae-eaters, they “clean” the reef of algae and enhance the growth and propagation of corals. Thus, despite increased predator pressure by groupers, coral grazing by parrotfish is enhanced by a shift in the species composition of parrotfish.

  13. Sorting CH5+ Vibrations

    The bonding in protonated methane (CH5+) has been hard to characterize, because even at low temperature, the hydrogen atoms flurry rapidly about the carbon center, rather than forming localized bonds. Recent experiments yielded the vibrational spectrum, which was assigned through classical trajectory calculations. Huang et al. (p. 60) present a fully quantum-mechanical interpretation of the spectrum based on ab initio calculations of dipole moment and potential energy surfaces. The results accord well with experiment and offer further insight into the nature of the three-center, two-electron bonding arrangement of this cation.

  14. Ozone and NOx

    The concentration of NOx (NO + NO2) is an important parameter in the ozone cycle of the lower troposphere. NOx catalyzes a chain of reactions that produces ozone photochemically during sunlight hours, and at night, it helps to destroy ozone. One key reaction of the nighttime cycle of ozone destruction is the hydrolysis of N2O5, a reaction that is slow in the gas phase but can be very rapid when it occurs heterogeneously on aerosols. Brown et al. (p. 67) report aircraft measurements that allowed them to determine the uptake coefficient for N2O5 on aerosol particles. The coefficient depends strongly on aerosol composition, particularly sulfate content. This result suggests that there is a stronger connection between anthropogenic sulfur and nitrogen oxide emissions than has been assumed, a possibility with important implications for the quantification of regional-scale ozone production.

  15. Shared Past

    Dendritic cells (DCs) and macrophages of the immune system have distinct and overlapping functions—DCs are pivotal in initiating and modulating immune responses through the uptake and presentation of antigen to T cells, whereas macrophages clear pathogens through phagocytosis and share some antigen-presenting capacity. Exactly how these cells are developmentally related is unclear. Fogg et al. (p. 83, published online 1 December 2005) identify a common progenitor cell that can be induced to generate DCs and macrophages in culture and produces subsets of both cells when transferred into mice. This common ancestry has many implications for understanding the developmental pathways required for the steady-state production of each type of cell and for their respective roles in immunity.